1. Field of the Invention
This invention relates to elastomers formed from aqueous emulsion which are made electrically conductive by the inclusion of metal-coated glass spheres.
2. Background Information
An emulsion which can form an electrically conductive silicone rubber is disclosed by Huebner et al. in U.S. Pat. No. 3,706,695, issued Dec. 19, 1972. They claim the use of from 8 to 35 weight percent of carbon black based upon the combined weight of siloxane and carbon black. Their Example 2 shows volume resistivity of the cured product varying from 2.11.times.10.sup.5 ohm-cm using 8.6 weight percent carbon black to 6.39.times.10.sup.3 ohm-cm using 30 weight percent carbon black.
U.S. Pat. No. 3,583,930, issued June 8, 1971, to Ehrreich et al. teaches that a plastic mass is made conductive by adding metal powders having a surface area to volume ratio of from 450 to 200,000 square feet/cubic foot. The maximum particle size is 100 mils (2.54 mm) preferably 40 mils (1.0 mm) while the minimum is 0.5 mil (0.013 mm) when a noble metal surface is used. Non-noble metals require a minimum size of about 5 mils. Included in plastic mass is elastomeric silicone resin.
U.S. Pat. No. 4,011,360, issued Mar. 8, 1977, to Walsh discloses the use of 75 to 98 parts by weight of electrically conductive particles in 2 to 25 parts by weight of a room temperature curing silicone rubber to obtain an electrically conductive flexible cured silicone rubber. The particle size may be between 5 micrometers to 10,000 micrometers. The mixtures cure upon exposure to moisture.